The invention relates to the art of welding with an electric arc and more particularly to an arc welder that is powered by a fuel efficient and portable power source, and even more particularly to an arc welder that is at least partially powered by a fuel cell.
The present invention incorporates the use of fuel cells of the general type described in U.S. Pat. Nos. 5,599,638; 5,656,388; 5,773,162; 5,795,496; 5,888,665; and 5,928,806; and PCT Patent Application Nos. WO 98/22989; WO 98/45694; WO 99/16137; and WO 99/39841. These patents and patent applications are also incorporated herein to describe the manufacture of the fuel cell components and operation of such fuel cells. U.S. Pat. Nos. 4,861,965; 4,972,064; 5,148,001; and 5,961,863 are also incorporated herein to describe a few of the welders that can be used with a fuel cell.
This invention relates to the field of arc welding, and more particularly to an improved arc welder that incorporates a fuel cell as an at least partial source of power for the arc welder.
Arc welders are typically powered by plugging the arc welding into an electrical outlet or having the arc welder equipped with a gas powered electric generator. Arc welders that are designed to receive power from an electric outlet are limited to use in a location that has an electric outlet which is rated to supply the needed current for operation of the arc welder. Operators of such arc welders need extension cords to increase the mobility of such arc welders. When the arc welder is used in a remote location or in a location that is not readily accessible to a power outlet or a power outlet having a needed current rating, the arc welder must be equipped with its own power source, such as a gas electric generator, to supply the required current to the arc welder. The gas generator is typically designed to be powered by a standard petroleum fuel source such as gasoline. In many operational environments, these two power source arrangements for arc welders are sufficient to satisfy the power demands of the arc welder.
Arc welders that are used in remote locations that are partially or totally enclosed or are not well ventilated may require special equipment during the welding operation. In such locations, a gas powered electric generator is used to supply power to the arc welder. During the operation of the gas powered generator, exhaust fumes are produced which can be unhealthy if breathed in sufficient concentrations. In additional, the gas powered generator produces noise during operation. Such noise could cause temporary hearing loss when operating the arc welder in a small enclosed environment for long periods of time. In addition to these operator health concerns, the operation of the gas powered electric generator produces pollutants which can be harmful and/or adversely affect the environment. These pollutants include noise pollution and combustion products from the combustion of fuel by the gas powered generator. Pollution concerns also exist for electric powered arc welders since the electricity is typically generated by coal burning generators and atomic power plants, both of which create their own environmental hazards. In addition to the pollution concerns of the energy sources, the cost of the energy continues to rise. As oil supplies and coal supplies continue to deplete worldwide, the cost of gasoline and electricity generated by coal burning generators will continue their unabated rise in cost. Rising energy costs generally slow or stunt growth in the industrial sectors.
Although these problems have existed for some time, there has heretofore been no viable alternative to gas powered electric generators for arc welders or arc welders powered by an electric outlet source. Battery powered arc welders are very bulky and have a limited life. Furthermore, once the battery has been discharged, the battery must be disposed of which is in-of-itself an environmental concern. In addition, many batteries require concentrated acids which can be harmful if such acid fumes are breathed in or if the acid contacts human skin. The acid is also an environmental pollutant requiring special and costly disposal. Solar power is another power source which is not feasible for use with an electric arc welder. The size of the solar panels necessary to generate the required amount of power are too large to use, especially in small environments. Furthermore, the solar panels require sunlight, thus on cloudy days or in enclosed environments, the solar battery will not produce the needed electric power. Solar power panels are also very expensive thereby making them cost prohibitive for use with arc welders. Wind powered generators are also not feasible due to their bulky construction and need for a consistent wind source. The bulkiness of batteries, solar panels, and wind powered generators compound the size problems of the arc welder. The electric circuitry in the welder is limited to a certain size by the power demands of the arc welder. Arc welders which require shielding gas must include bulky canisters to supply the shielding gas. The combination of bulky shielding gas canisters with a bulky power source would make the arc welder unwieldy for use in many environments.
In view of the problems associated with alternative power sources for electric arc welders, there is a need for an improved power source that is environmentally friendly, can be safely use in a wide variety of locations, and is simple and safe to operate.
The present invention relates to a method and apparatus of arc welding together metal plates, and more particularly a method and apparatus for arc welding that incorporate a fuel cell as an energy source to totally or partially power the arc welder.
In accordance with the preferred embodiment of the present invention, there is provided a fuel cell power supply with a positive and negative terminal, a welding current circuit which applies a welding current across a welding electrode and a workpiece. The fuel cell is an electrochemical cell in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. In one embodiment, an organic/air fuel cell is used to oxidize an organic fuel to carbon dioxide at an anode while air or oxygen is reduced to water at a cathode. Fuel cells employing organic fuels are extremely attractive because of the high specific energy of the organic fuels. In another embodiment, the fuel cell is an xe2x80x9cindirectxe2x80x9d or xe2x80x9creformerxe2x80x9d fuel cell or a xe2x80x9cdirect oxidationxe2x80x9d fuel cell. In an indirect fuel cell, the fuel is catalytically reformed and processed. For organic fuels, the fuel is catalytically reformed and processed into carbon monoxide-free hydrogen, with the hydrogen so obtained oxidized at the anode of the fuel cell. In a direct oxidation fuel cell, the fuel is directly fed into the fuel cell without any previous chemical modification where the fuel is oxidized at the anode. Direct oxidation fuel cells do not require a fuel processing stage. As a result, direct oxidation fuel cells are generally less complicated and are smaller in size than indirect fuel cells.
In accordance with another aspect of the present invention, the fuel cell includes high-surface-area electro-catalytic anodes and/or cathodes. In one embodiment, the fuel cell anode and/or cathode fabrication includes a high surface-area carbon-supported metal powder. In one aspect of this embodiment, alloy powder combined with a TEFLON binder is applied to a carbon fiber-based support to yield a gas diffusion anode and/or cathode. In another embodiment, the anode and/or cathode is used for gas and/or liquid feeds. In still another embodiment, the anode and/or cathode is very porous to allow for proper wetting of the pores.
In accordance with still another embodiment of the present invention, the anode and/or cathode of the fuel cell is coated by a substance that improves the wetting properties of the electrode. In accordance with this specific aspect of the invention, a compound including perfluorinated sulfonic acid is coated on the anode and/or cathode to increase the wetting properties of the anode and/or cathode. The coating decreases the interfacial tension of the liquid/catalyst interface and leads to a more uniform wetting of the anode and/or cathode pores and particles by the liquid fuel solution, yielding enhanced utilization of the electrocatalyst. The coating can also provide ionic continuity with the solid electrolyte membrane and permit efficient transport of protons or hydronium ions generated by the fuel oxidation reaction. The coating may further facilitate in the release of carbon dioxide from the pores of the anode and/or cathode. By using a perfluorinated sulfonic acid, anionic groups are not strongly adsorbed on the anode and/or cathode/electrolyte interface. Consequently, the kinetics of electro-oxidation of methanol are more facile than in sulfuric acid electrolyte. Other hydrophilic proton-conducting additives with the desired properties which can be alternatively used or used in combination with perfluorinated sulfonic acid include montmorrolinite clay, alkoxycelluloses, cyclodextrins, mixtures of zeolites, and/or zirconium hydrogen phosphate.
In accordance with another aspect of the present invention, a liquid fuel is used in the fuel cell. In one embodiment, the liquid fuel undergoes clean and efficient electro-chemical oxidation within the fuel cell. For direct oxidation fuel cells, the efficient utilization of organic fuels is governed by the ease by which the organic compounds are anodically oxidized within the fuel cell. In one embodiment, the organic fuel includes methanol, formaldehyde, formic acid, trimethoxymethane, dimethoxymethane and/or trioxane.
In accordance with yet another aspect of the present invention, the fuel cell is a direct type liquid feed fuel cell which does not require an acid electrolyte. In one embodiment, a solid polymer electrolyte membrane is used to eliminate the need for the acid electrolyte. In another embodiment, the solid polymer electrolyte membrane is used in combination with a battery-type anode that is porous and is capable of wetting the fuel. In still another embodiment, a battery-type anode structure and a cathode are bonded to either side of the solid polymer electrolyte membrane. A solution of an organic feed which is substantially free of acid is circulated past the anode side of the assembly. The solid polymer membrane is formulated to have excellent electrochemical and mechanical stability, high ionic conductivity, and functions both as an electrolyte and as a separator. Furthermore, when using an organic feed such an methanol, the kinetics of electro-oxidation of the organic feed and electro-reduction of air or oxygen are more facile at an anode and/or cathode/membrane-electrolyte interface as compared to an anode and/or cathode/sulfuric acid interface. In a further embodiment, the solid polymer electrolyte is a proton-conducting cation-exchange membrane. In one specific aspect of this embodiment, the membrane includes tetrafluoroethylene, perflourinated sulfonic acid polymer, a polystyrene sulfonic acid, a poly (vinylidene fluoride), a polyhydrocarbon sulfonic acid, and/or a co-polymer of tetrafluoroethylene and perfluorovinylether sulfonic acid. In another specific aspect of the embodiment, membranes of modified perflourinated sulfonic acid polymer, polyhydrocarbon sulfonic acid, polyhydrocarbon sulfonic acid which can be used includes, but are not limited to, a sulfonated polyether ether ketone, and/or a poly (phenylene ether sulfone). In another embodiment, the exchange membrane is a composite of two or more different kinds of proton exchange membranes. In still another embodiment, the membrane permits operation of the fuel cell at temperatures at least up to 120xc2x0 C. In still yet another embodiment, the fuel cell is substantially free of expensive corrosion-resistant components in the fuel cell due to the absent of an acidic electrolyte. In still another embodiment, the membrane thickness is about 0.05-1 mm.
In accordance with a further aspect of the present invention, the anode of the fuel cell is formed from high surface area particles of platinum-based alloys of noble and non-noble metals. In one embodiment, binary and ternary compositions can be used for the electro-oxidation of organic fuels. In another embodiment, platinum alloy, with compositions varying from 10-90 percent platinum, makes up the anode. In one specific aspect of this embodiment, the platinum alloy includes ruthenium, tin, iridium, osmium, and/or rhenium. In yet another embodiment, all or part of the platinum in the platinum alloy is substituted for palladium, tungsten, rhodium, iron, cobalt, titanium, iridium, chromium, manganese, molybdenum, niobium, zirconium, osmium, titanium oxide and/or nickel. In still another embodiment, the platinum alloy particles are in the form of fine metal powders, i.e., xe2x80x9cunsupportedxe2x80x9d, and/or are supported on high surface area material. In one specific aspect, the high surface area material includes a carbon material. In another embodiment, the platinum alloy is loaded in the electrocatalyst layer in the range of about 0.05-4.0 mg/cm2. In still another embodiment, particles of titanium oxide, iridium and/or osmium are added to the platinum alloy to improve fuel cell performance. In yet another embodiment, the average particle size of the particles on the anode is about 0.5-8 microns.
In accordance with a yet a further aspect of the present invention, the cathode of the fuel cell is formed from particles which include platinum, supported and/or unsupported, to the proton permeable membrane. In one embodiment, the platinum particles are supported on a carbon containing material. In another embodiment, the cathode includes a material to increase the hydrophobicity of the cathode. In one aspect of this embodiment, the material to increase the hydrophobicity includes tetrafluoroethylene. In another embodiment, the platinum particles are loaded in the electrocatalyst layer in the range of about 0.05-4.0 mg/cm2. In still another embodiment, the average particle size of the particles on the cathode is about 0.5-8 microns.
In accordance with another aspect of the present invention, the fuel cell is a regenerative fuel cell. In one embodiment, the fuel cell reduces carbon dioxide to an oxygenated hydrocarbon and oxygen. In another embodiment, the oxygenated hydrocarbons include methyl alcohol, methyl formate, formaldehyde and/or formic acid.
In accordance with yet another aspect of the present invention, a plurality of fuel cells are stacked together to increase the voltage and/or current generated by the fuel cells. In one embodiment, a plurality of fuel cells are connected together in parallel. In another embodiment, a plurality of fuel cells are connected together in series
In accordance with still yet another aspect of the present invention, one or more of the products of the fuel cell are at least partially used as a shielding gas for the arc welder. In one embodiment, the shielding gas produced from the fuel cell includes carbon dioxide and/or carbon monoxide. In another embodiment, a dehumidifier, condenser and/or scrubber are used to remove undesired gases and/or liquids from the product gas prior to directing the product gas to the welding pool. In still another embodiment, a shielding gas controller is used to regulate the amount of shielding gas directed to the workpiece and/or to control the pressure of the shielding gas to the workpiece.
In accordance with another aspect of the present invention, the welding electrode is a consumable electrode. In one embodiment, the consumable electrode is a flux cored electrode that includes a flux system within the cored electrode to provides a shielding gas and/or a desired slag during the welding process. In one aspect of this embodiment, the consumable cored electrode includes alloy metals in the core so as to obtain a weld bead composition which is substantially similar to the composition of the workpieces being welded together. A weld bead having a composition which closely matches the composition of the workpieces forms a strong, durable, high quality weld bead. In another embodiment, the consumable electrode is a flux coated electrode or a solid metal electrode.
In accordance with still another aspect of the present invention, the welding circuit is designed for use in a short circuit arc welder. In one embodiment, the welding circuit includes a first circuit for controlling the current flow during the short circuit condition wherein the molten metal at the end of the consumable cored electrode is primarily transferred by a transfer current into a molten metal pool by surface tension action. In one specific aspect of this embodiment, the transfer current includes a high current pinch pulse across the shorted melted metal which helps facilitate the transfer of the molten metal from the electrode to the weld pool. In still another embodiment, the welding current circuit includes a second circuit to create a melting current. In one specific aspect of this embodiment, the melting current is a high current pulse which is passed through the arc. Preferably, the high current pulse has a preselected amount of energy or wattage used to melt a relatively constant volume of metal at the end of the consumable electrode when the electrode is spaced from the welding pool. In still yet another embodiment, the second circuit of the welding current circuit provides a high energy boost during the initial portion of the arcing condition. In one specific aspect of this embodiment, the high current boost has a preselected I(t) area or energy for melting a relatively constant volume of metal on the end of the consumable wire when the wire is spaced from the welding pool. In another specific aspect of this embodiment, the energy created during the high current boost or plasma boost is sufficient to create a spherical metal ball having a diameter of no more than twice the diameter of the welding wire. In still a further embodiment, after the initial high current boost, a high current is maintained for a preselected period of time and then subsequently reduced so that the desired amount of energy or wattage is applied to the electrode to melt the desired volume of the electrode. In one specific aspect of this embodiment, the reduction of the high current is in the form of a delayed current over a period of time. In another embodiment, the welding current circuit limits the amount of energy directed to the electrode so as to prevent the unnecessary melting of the workpiece ends.
In accordance with another aspect of the present invention, the welding current circuit includes a circuit to produce a background current. In one embodiment, the background current is a low level current which is maintained just above the level necessary to sustain an arc after the termination of a short circuit condition. In another embodiment, the background current is maintained throughout the welding cycle to insure that the arc is not inadvertently extinguished during welding.
In accordance with still another aspect of the invention, the welding circuit includes a controller for shifting between polarity during the welding process. In one embodiment, the duration of the positive and negative polarity pulse during a single welding cycle is the same. In another embodiment, the duration of the positive and negative polarity pulse during a single welding cycle is different. In still another embodiment, a positive polarity pulse occurs during a single welding cycle and a negative polarity pulse occurs during anther welding cycle. In yet another embodiment, the controller is software controlled.
In accordance with yet another aspect of the present invention, an STT welder of The Lincoln Electric Company or STT short circuit welding process is used. In one embodiment, the STT process is used with a cored electrode. In another embodiment, the STT process is used with a consumable electrode and the polarity through the electrode negative. When using the electrode negative process of the STT welder, the workpiece puddle is hot and the cooling of the puddle requires time allowing the bead to be pulled back. In one aspect of the embodiment, the background current is reduced to reduce the heat in the puddle. This current correction decreases the amount of heat in the total welding process. By reversing the polarity of the STT welder to an electrode positive condition, the workpiece puddle may become too cold. To overcome this weld puddle cooling, the STT welder or process shifts between the standard electrode negative polarity to electrode positive polarity during the total welding process. In this manner the heat is controlled without changing the level of the background current. The heat of the puddle is controlled to a selected temperature by adjusting the ratio of negative electrode to positive electrode welding.
In accordance with another embodiment of the present invention, the electrode is a non-consumable electrode. In one embodiment, the non-consumable electrode includes tungsten.
In accordance with yet another aspect of the present invention, the welding circuit is designed for TIG welding. In one embodiment, the welding circuit shifts polarity during the welding process. In another embodiment, the duration of the positive polarity pulse and the negative polarity pulse during a welding cycle is the same. In yet another embodiment, the duration of the positive polarity pulse and the negative polarity pulse during a welding cycle is different. In still another embodiment, the welding circuit convents direct current into alternating current. In one specific aspect of this embodiment, the current alteration is accomplished by high speed power switches with at least one switch being conductive when at least one other switch is non-conductive, and visa-versa. In another specific aspect of this embodiment, the welding circuit includes a high reactance reactor or choke with first and second portions, and the first portion is connected across the power supply in a negative polarity direction for a heating cycle and then reversing the procedure by applying the second portion of the reactor or choke across the workpiece in the opposite direction. In still another specific aspect of this embodiment, the current alteration is accomplished by software control.
In accordance with still yet another embodiment of the present invention, the welding circuit includes boost-buck circuit to increase the voltage from the welding power supply to the electrode.
The primary object of the present invention is the provision of an arc welding system and method which forms a high quality weld bead between two metal plates.
Another object of the present invention is the provision of an arc welding system and method which includes a fuel cell to at least partially supply power to generate an arc between an electrode and the workpiece.
Still another object of the present invention is the provision of an arc welding system and method which is environmentally friendly.
Yet another object of the present invention is the provision of an arc welding system and method which reduces noise and/or air pollution during operation.
A further object of the present invention is the provision of an arc welding system and method which is portable and can be used in a wide variety of environments.
Still a further object of the present invention is the provision of an arc welding system and method which includes a direct oxidation fuel cell.
Yet a further object of the present invention is the provision of an arc welding system and method that includes a fuel cell that produces one or more product gasses that can be at least partially used as a shielding gas.
Another object of the present invention is the provision of an arc welding system and method which includes a fuel cell that uses an organic liquid feed.
Yet another object of the present invention is the provision of an arc welding system and method that includes a plurality of stacked fuel cells.
Still another object of the present invention is the provision of an arc welding system and method which accurately tracks a desired current profile during the welding of a workpiece.
Another object of the present invention is the provision of an arc welding system and method which includes a fuel cell having at least one proton conducting membrane positioned between an anode and cathode of the fuel cell.
Yet another object of the present invention is the provision of an arc welding system and method which includes a fuel cell having at least one proton conducting membrane which inhibits the migration through the membrane of the organic feed for the fuel cell.
Still yet another object of the present invention is the provision of a short circuiting arc welding system and method for applying a controlled amount of energy to the electrode to form a weld bead on the workpiece.
A further object of the present invention is the provision of an arc welding system and method which produces a weld bead having a composition which is substantially similar to the composition of the workpiece.
Yet another object of the present invention is the provision of an arc welding system and method which uses a cored electrode to form a high quality weld bead.
A further object of the invention is the provision of an arc welding system and method which changes the polarity of the weld current during a welding process.
Another object of the present invention is the provision of an arc welding system and method which controls the heat of the weld puddle by adjusting the ratio of electrode positive current to electrode negative current, either during a cycle or from one cycle to the next cycle.
Still another object of the present invention is the provision of an arc welding system and method which increases the voltage to the electrode.
These and other objects and advantages will become apparent to those skilled in the art upon reading the following description taken together with the preferred embodiment disclosed in the accompanied drawings.